Implement name_list.

This patch implements the `name_list` command of Namecoin.  It also includes https://github.com/libcoin/libcoin/pull/72 because that is necessary to actually test it with some wallet.  I can squash the commits to get a clean history after the wallet fix is merged upstream - let me know if I should do so.

Note that `name_list` is currently added to `libcoind` without authorisation - it can't steal anything, so it is not critical.  Since `listtransactions` uses authorisation, on the other hand, it may be more consistent to also do that for `name_list`.  Let me know if I should adapt the patch.

Finally, to get the expiration result matching `namecoind`, I had to correct an off-by-one error.  It seems that what the SQLite database stores as `count` is the *blockheight + 1*.  Please confirm that before merging, otherwise there may be another problem somewhere else.